When the bobbins on the rotating spindles of a spinning frame have been filled with yarn, the operation of the spinning frame is stopped and all of the filled bobbins are doffed and replaced with empty bobbins to be filled during subsequent operation of the spinning frame. Since this doffing and donning operation must be carried out at relatively frequent intervals, and since the manual doffing and donning of bobbins is both difficult and time consuming, some manufacturers of modern spinning frames also produce complementary automatic doffing machines which are specifically designed as an intergral part of a particular spinning frame. By designing a spinning frame and a doffing machine for integral use with one another, it is usually feasible to control the doffing machine electrically, using carefully designed and relatively safe electrical components (e.g. solenoid operated valves) operated by the existing electrical system in the spinning frame. An example of an integrated spinning frame and doffing equipment is disclosed in U.S. Pat. No. 3,609,952, issued Oct. 5, 1971.
However, there are a very large number of spinning frame currently in use which are of varying types, and which were not designed for integral use with automatic doffing machines. In the majority of instances, these spinning frames are doffed manually, with a workman simply walking along a row of spinning frame spindles and manually removing the full bobbins and placing empty bobbins on the spindles, all of which is burdensome for the workman and requires a significant expense in terms of labor.
In an effort to deal with the problem of manually doffing and donning bobbins in conjunction with a wide variety of different spinning frames, a number of semi-automatic and automatic doffing machines have heretofore been proposed, and these machines have met with varying degrees of success. For example, U.S. Pat. No. 2,175,349, issued Mar. 30, 1935, to Escursell-Prat, discloses a doffing machine which is manually pushed along a spinning frame with a combination of cams, gears and similar mechanical elements being used to control and operate the various components of the machines. While semi-automatic, mechanical operation has the advantages of simplicity and safe operation, it also suffers a significant disadvantage in that it is not entirely reliable in operation, particularly when it is designed to carry out predetermined sequential steps in doffing and donning the bobbins. More specifically, where a cam or similar operating element is relied upon to operate a plurality of follower members in a predetermined sequence, it is not uncommon for the sequence cam to fail to operate properly one or more of the followers, whereupon one or more of the steps in the sequential operation will not be carried out so that the doffing machine may jam or otherwise become inoperative until repaired. This problem is particularly acute where the sequence cam is moved or operated by a pneumatic motor receiving pressurized fluid from the existing mill compressed air system because even small variations in the pressure of such air system will adversely affect the operating relationship between the sequence cam and the followers therefor, as for example by increasing or decreasing the dwell time during which a follower is engaged by the moving sequence cam.
Some prior art doffing machines rely upon electrical power to operate or control some of the elements thereof, such as U.S. Pat. No. 2,886,940, issued May 19, 1959, U.S. Pat. No. 3,895,482, issued July 22, 1975, and U.S. Pat. No. 3,442,072, issued May 6, 1969. However, electrical systems used in doffing machines have two significant practical drawbacks. First, since the doffing machine is operated independently of the spinning frame, it must have its own source of electrical energy that is provided continuously during its travel along the entire length of a spinning frame. Customarily, such electrical energy is supplied by an electrical cord that is connected at one end to an available outlet at or near the spinning frame, and this electrical cord must then trail along the spinning room floor behind the doffing machine as it moves along the spinning frame, thereby creating a safety hazard to the operators of the spinning room equipment and other personnel who must walk along the floor space where the exposed electrical cord is located. Additionally, to the extent that an electrical control system for the doffing machine includes electrical switches having contacts which are opened and closed to control the operation of various elements of the doffing machine, the usual concentration of lint which is present in the environment of any spinning room may result in the electrical contacts becoming coated with a layer of such lint so that the contacts may not operate properly and may create a fire hazard.
In accordance with the present invention, the aforementioned drawbacks are eliminated by providing a doffing machine having a unique pneumatic control system for safely and reliably operating a plurality of coordinated movements in a predetermined sequence, with any particular step in the sequence occurring only after a predetermined preceding step or steps have been completed.